Bartonellosis – Diagnostics – Overview of Information and Clinical Research

Understanding bartonellosis begins with recognizing who might be carrying these hidden bacteria and knowing when to seek medical attention. This group of infections can affect anyone, but certain people face higher risks depending on their exposure to cats, insects, or specific geographic areas.

Introduction: Who Should Seek Testing and When

Bartonellosis is a group of infectious diseases caused by bacteria from the Bartonella genus, which are tiny organisms that can live inside your blood cells and the cells lining your blood vessels. While there are at least 22 known species of Bartonella bacteria, only about 15 of them are known to cause illness in humans.^[1]^[4]

Anyone who has been scratched or bitten by a cat, especially a kitten, should consider testing if they develop unusual symptoms. Cat scratch disease, caused by Bartonella henselae, is the most common form of bartonellosis in the United States, affecting approximately 20,000 people each year.^[3] Children between the ages of 5 and 9 are particularly affected, as they are more likely to play with kittens and may not understand how to handle them gently.^[2]^[5]

People living in crowded conditions without access to proper hygiene should be aware of trench fever, which is transmitted through body lice and caused by Bartonella quintana. This infection has historically affected soldiers in trenches during wartime but continues to appear in populations experiencing homelessness or living in poverty-stricken areas with poor sanitation.^[6]^[7]

If you have traveled to the Andes mountains, particularly in Peru, Colombia, or Ecuador, you should seek testing if you develop sudden high fever or unusual skin nodules. These areas are home to sand flies that carry Bartonella bacilliformis, which causes Carrión’s disease. This infection can be life-threatening without treatment, especially during its acute phase known as Oroya fever.^[2]^[5]

⚠️ Important

People with weakened immune systems, including those with HIV/AIDS, cancer patients undergoing treatment, or organ transplant recipients, face a much higher risk of severe Bartonella infections. These individuals can develop serious complications such as bacillary angiomatosis, which causes tumor-like masses of blood vessels, or heart valve infections called endocarditis. If you have a compromised immune system and develop persistent fever, unusual skin growths, or heart-related symptoms, seek medical attention promptly.^[4]^[5]

Veterinarians and veterinary team members should be particularly vigilant about testing, as research has found that up to 50 percent of veterinary professionals tested positive for one or more Bartonella species. These healthcare workers are regularly exposed to animal blood, scratches, and bites, putting them at substantially higher risk than the general population.^[8]

You should consider diagnostic testing if you experience swollen, painful lymph nodes that persist for weeks, especially if you’ve recently been around cats. Other warning signs include persistent fever that comes and goes, unexplained fatigue lasting months, severe headaches, muscle aches, or unusual skin bumps or rashes. For children and adults alike, changes in behavior, difficulty concentrating, or new neurological symptoms following possible exposure warrant immediate medical evaluation.^[3]^[5]

Classic Diagnostic Methods for Identifying Bartonellosis

Diagnosing bartonellosis requires laboratory confirmation because the symptoms can be nonspecific and similar to many other conditions. Your doctor cannot diagnose this infection based on symptoms alone, even when you have a clear history of cat exposure or insect bites.^[3]

Serological testing is one of the most commonly used diagnostic methods. This involves taking a blood sample and looking for antibodies your immune system has produced in response to Bartonella infection. The most frequently employed test is called an immunofluorescent antibody (IFA) assay, which can detect both IgM antibodies (indicating recent infection) and IgG antibodies (which can persist long after infection).^[3]^[9]

However, serological testing has significant limitations. Studies have found that positive antibody levels were detected in only 30 percent of patients whose Bartonella infection was later confirmed through other methods. This means that many people with active infections might receive false negative results. Additionally, antibodies to one Bartonella species can cross-react with antibodies to other species, making it difficult to identify exactly which type of bacteria is causing the illness.^[3]^[14]

Cross-reactions can also occur with antibodies to other bacteria, including Coxiella burnetii (which causes Q fever), Chlamydia, and certain rickettsial infections. This means a positive test might not definitively prove Bartonella infection. Western blot tests appear to have greater specificity, meaning they are better at distinguishing Bartonella from other similar infections, but they are not always readily available.^[3]

For cat scratch disease specifically, doctors may diagnose the condition clinically when patients show typical signs and symptoms combined with a compatible exposure history. This means if you have the characteristic swollen lymph nodes near a cat scratch site, along with a clear history of being scratched by a cat, your doctor might diagnose cat scratch disease without laboratory confirmation.^[14]

Polymerase chain reaction (PCR) testing offers another diagnostic approach. This molecular technique can detect and amplify the DNA of various Bartonella species in blood samples, spinal fluid, or tissue samples. PCR may be the most reliable test for Bartonella infection, especially given the cross-reactivity problems with antibody tests. However, the sensitivity of PCR is not optimal for blood samples, meaning it might miss infections even when bacteria are present.^[3]^[9]

PCR testing is particularly useful for analyzing lymph node aspirates, though doctors generally do not recommend aspirating lymph nodes except to relieve severe pain and swelling or when the diagnosis is unclear. When patients need heart valve replacement surgery due to endocarditis, the removed valve tissue can be tested using PCR to confirm Bartonella infection.^[14]

Bacterial culture is possible for Bartonella, but these bacteria are fastidious, meaning they are extremely difficult to grow in laboratory conditions. They grow very slowly, requiring cultures to be held for a minimum of 21 days. Standard culture media often proves insensitive for detecting these bacteria. Providers should alert the microbiology laboratory when Bartonella is suspected so technicians can optimize conditions for growth.^[3]^[14]

For patients with skin lesions or unusual growths, a skin biopsy can be performed. When the tissue sample is examined under a microscope using special staining techniques (particularly the Warthin-Starry silver stain method), doctors can sometimes see the Bartonella bacteria adhering to cells. This histological examination can help confirm the diagnosis, especially in cases of bacillary angiomatosis or verruga peruana.^[9]^[5]

Blood smears can reveal important clues in Carrión’s disease. During the acute phase called Oroya fever, peripheral blood smears show many bacilli attached to red blood cells, along with abnormally shaped red blood cells and very low platelet counts. These findings, combined with the patient’s travel history to endemic areas, strongly suggest Bartonella bacilliformis infection.^[9]

It is important to tell your healthcare provider about your medical history, including whether you have cats at home, have been around cats recently, live in crowded conditions, have traveled to South America, or have any conditions affecting your immune system. This information helps your doctor decide which diagnostic tests are most appropriate and interpret the results correctly.^[5]

⚠️ Important

One important consideration with Bartonella testing is that serological tests may remain positive for years even after successful treatment and complete recovery. This makes it difficult to use antibody tests to determine whether treatment has been effective or whether someone has an active infection versus a past infection. Animal studies have also shown that many healthy individuals may test positive for Bartonella antibodies without ever recalling symptoms of infection, suggesting that not all exposures result in illness.^[3]

Diagnostics for Clinical Trial Qualification

Clinical trials studying Bartonella infections or their treatments typically require specific diagnostic criteria to ensure participants truly have the infection being studied. These enrollment standards are usually more rigorous than those used in routine clinical practice.

Most clinical trials would require laboratory confirmation of Bartonella infection rather than accepting clinical diagnosis alone. This typically means participants must have positive serological tests (IFA showing specific antibody levels), positive PCR results detecting Bartonella DNA, or positive bacterial cultures. Some trials might require multiple positive tests or serial testing to confirm that the infection is active rather than representing past exposure.^[3]^[9]

For trials focused on cat scratch disease, researchers might use both histological and epidemiological criteria. Histological criteria would involve microscopic examination of tissue samples showing characteristic changes consistent with Bartonella infection. Epidemiological criteria would include documented exposure to cats, particularly kittens, and the presence of characteristic symptoms such as regional lymph node enlargement near a scratch site.^[2]

Trials studying treatments for endocarditis caused by Bartonella would likely require confirmation through multiple methods, potentially including positive blood cultures, positive PCR from blood or heart valve tissue, positive serology with high antibody levels, and imaging evidence of heart valve damage or vegetations visible on echocardiogram.^[9]

Because serological tests can cross-react with other infections and remain positive long after recovery, clinical trials might employ DNA sequencing to definitively identify the specific Bartonella species present. This level of precision ensures that researchers are studying the correct pathogen and can accurately assess treatment effectiveness.^[3]

Trials might also exclude participants who have recently received antibiotic treatment, as this could affect bacterial load and make it more difficult to culture bacteria or detect bacterial DNA. Baseline testing before treatment begins would establish the presence and extent of infection, while follow-up testing at specified intervals would assess treatment response and clearance of the bacteria.

Prognosis and Survival Rate

Prognosis

The outlook for people with bartonellosis varies considerably depending on which species causes the infection and the person’s immune system status. For immunocompetent individuals (those with normal immune function) who develop cat scratch disease, the prognosis is generally excellent. The infection is self-limiting in most cases, meaning it resolves on its own within two to four months without requiring treatment. Lymph node swelling typically persists for two to twelve months but eventually subsides completely.^[4]^[13]

However, complications can occur even in otherwise healthy people. About 20 percent of patients with Bartonella bacilliformis infection develop neurological involvement, including altered mental status, agitation, coma, difficulty with coordination, spinal inflammation, or paralysis. When neurobartonellosis occurs, the prognosis becomes much more guarded, with approximately 50 percent mortality even with treatment.^[9]

Immunocompromised patients face substantially worse outcomes. Those with HIV/AIDS, cancer undergoing chemotherapy, or taking immunosuppressive medications after organ transplants can develop severe, progressive, and disseminated disease. These individuals are at risk for bacillary angiomatosis and bacillary peliosis, both of which can be fatal if left untreated. With appropriate antibiotic therapy, 95 percent of patients respond to treatment, though immunocompromised individuals often require extended treatment courses lasting three months or longer to prevent relapse.^[8]^[9]

Factors affecting disease progression include prompt diagnosis and treatment initiation, the patient’s immune status, the specific Bartonella species involved, and whether complications such as endocarditis have developed. Heart valve infection represents one of the most serious complications, often requiring both prolonged antibiotic therapy and surgical valve replacement. Endocarditis caused by Bartonella is frequently only diagnosed when tissue is obtained during heart valve replacement surgery.^[6]^[11]

Survival rate

Without treatment, Bartonella bacilliformis infection during the acute Oroya fever phase carries a mortality rate higher than 40 percent and has been reported as high as 90 percent in some outbreaks. This makes it the most deadly Bartonella species affecting humans. The acute phase typically lasts two to four weeks, during which the bacteria destroy red blood cells, causing severe anemia and creating an immunosuppressed state that leaves patients vulnerable to overwhelming secondary infections.^[9]^[11]

For endocarditis caused by Bartonella species, there is an 11.9 percent mortality rate globally. This complication most commonly affects the mitral and aortic heart valves and carries a high risk of embolization (pieces of infected material breaking off and traveling to other organs). While no known deaths have been specifically associated with the fever aspect of trench fever, the disease can progress to endocarditis in some cases.^[6]

In immunocompromised patients, bacillary angiomatosis takes a more severe form and can lead to death if left untreated. However, when diagnosed promptly and treated with appropriate antibiotics, the vast majority of these patients recover. The chronic phase of Carrión’s disease (verruga peruana) is generally benign and rarely causes death, though the skin nodules can persist for months or even years without treatment.^[6]^[9]

For uncomplicated cat scratch disease in immunocompetent individuals, mortality is extremely rare. Most patients fully recover without any long-term health consequences. The infection does not typically cause chronic bacteremia or persistent symptoms in people with healthy immune systems, though recent case reports suggest that some individuals may experience chronic intravascular infection lasting months to years with a range of symptoms including neuropsychiatric manifestations.^[3]^[13]

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